Many wireless local area networks (WLANs), such as those based on a communication protocol that is compatible with an IEEE 802.11 standard (which is sometimes referred to as ‘Wi-Fi’), involve contention-based distributed access systems. For example, Wi-Fi often uses single-user transmission via enhanced distributed channel access or EDCA. In particular, the WLANs are usually contention based because they typically utilize unlicensed frequency bands or spectra, which are unpredictable and are often subject to interference. The unpredictability of the interference can make coordination across multiple electronic devices (which are sometimes referred to as ‘stations’ or STAs) challenging (especially for an unmanaged WLAN), and can result in the failure of a collision free period (CFP). However, the use of fully distributed channel access can allow a simpler access point (AP) and a simpler network deployment (relative to a cellular network), which can make it easier and cheaper to deploy a WLAN.
Recently, contention-free multi-user transmission for uplink communication from STAs to an AP has been proposed in the IEEE 802.11ax standard. This approach can dramatically change how an electronic device accesses the communication medium. In particular, an electronic device can transmit without contending for the communication medium. Instead, an access point may manage access to the communication medium for the electronic device, and may grant transmission opportunities to the electronic device using a trigger frame (which is sometimes referred to as ‘trigger-based access’ or ‘trigger-based channel access,’ e.g., uplink multi-user transmission). During trigger-based uplink channel access, an access point may: sense the communication medium and, as needed, perform a back-off operation on behalf of potential uplink trigger-access-enabled electronic devices; define the uplink physical layer convergence protocol (PLPC) protocol data unit (PDU) or PPDU duration for the electronic device; and decide the modulation and coding scheme (MCS) for the electronic device.
In principle, if more electronic devices rely on trigger-based access, then the overall contention in the WLAN can be reduced. Consequently, trigger-based access is often expected to result in improved communication performance. However, in practice, this is not always the case. In particular, depending on overhead required for the trigger-based access and on a distance between the electronic device and the access point, single-user EDCA may be preferred to multi-user uplink trigger-based access.
For example, for the same transmission opportunity (TXOP) in a low contention environment, trigger-based access typically results in poorer communication performance. This is because, in contrast with EDCA, the overhead from the multi-STA block acknowledgement (M-BA) frame in each TXOP can grow linearly with the number of electronic devices in trigger-based access (i.e., each electronic device may be acknowledged more frequently). Moreover, Orthogonal Frequency-Division Multiple Access (OFDMA) in multi-user uplink trigger-based access can outperform single-user EDCA as the distance between electronic devices and the access point increases (i.e., the far-distance case) because multi-user uplink trigger-based access typically uses a higher MCS, which can increase the overall throughput. Therefore, it can be difficult to select a channel access policy for an electronic device in a WLAN.